In recent years, a semiconductor device using silicon carbide (SiC) has been regarded as a promising next-generation switching element capable of achieving higher breakdown voltage, lower loss, and higher resistance to heat, and is expected to be applied in a power semiconductor device such as an inverter. However, the silicon carbide semiconductor device has many problems to be solved.
In an MOSFET formed by using silicon carbide, reducing the sheet resistance of a source region and reducing resistance of an ohmic contact between the source region and an electrode are important for reducing loss in an energized state. Hence, the source region should have a high impurity concentration. However, the high impurity concentration in the source region increases a leakage current in a gate oxide film on the source region.
The gate oxide film may be formed by process such as thermal oxidation process or chemical vapor deposition (CVD) process (as described in patent literatures 1 to 4, for example). The thermal oxidation process includes wet oxidation performed in an atmosphere containing oxygen (O2) and water vapor (H2O), and dry oxidation performed in an atmosphere containing oxygen but not containing water vapor.